LM3421_09 Datasheet, PDF (1/24 Pages) National Semiconductor (TI) – N-Channel Controllers for Constant Current LED Drivers

January 26, 2009
LM3421, LM3423
N-Channel Controllers for Constant Current LED Drivers
General Description
The LM3421/LM3423 devices are versatile high voltage LED
driver controllers. With the capability to be configured in a
Buck, Boost, Buck-Boost (Flyback), or SEPIC topology, and
an input operating voltage rating of 75V, these controllers are
ideal for illuminating LEDs in a very diverse, large family of
applications.
Adjustable high-side current sense with a typical sense volt-
age of 100mV allows for tight regulation of the LED current
with the highest efficiency possible. Output LED current reg-
ulation is based on peak current-mode control with predictive
Off-Time Control. This method of control eases the design of
loop compensation while providing inherent input voltage
feed-forward compensation.
The LM3421/LM3423 include a high-voltage startup regulator
that operates over a wide input range of 4.5V to 75V. The
internal PWM controller is designed for adjustable switching
frequencies of up to 2.0MHz, thus enabling compact solu-
tions. Additional features include: “zero” current shutdown,
precision reference, logic compatible DIM input suitable for
fast PWM dimming, cycle-by-cycle current limit, and thermal
shutdown.
The LM3423 also includes an LED output status flag, a fault
flag, a programmable fault timer, and a logic input to select
the polarity of the dimming output driver.
Features
■ ^V_IN ^{range from 4.5V to 75V}
■ ^{2% Internal reference voltage (1.235V)}
■ ^{Current sense voltage adjustable from 20mV}
■ ^{High-side current sensing}
■ 2Ω MOSFET gate driver
■ ^{Dimming MOSFET gate driver}
■ ^{Input under-voltage protection}
■ ^{Over-voltage protection}
■ ^{Low shutdown current, I}_Q ^{< 1µA}
■ ^{Fast (50kHz) PWM dimming}
■ ^{Cycle-by-cycle current limit}
■ ^{Programmable switching frequency}
■ ^{LED output status flag (LM3423 only)}
■ ^{Fault timer pin (LM3423 only)}
■ ^{TSSOP EP 16-lead package (LM3421)}
■ ^{TSSOP EP 20-lead package (LM3423)}
Applications
■ ^{LED Drivers}
■ ^{Constant-Current Buck-Boost Regulator}
■ ^{Constant-Current Boost Regulator}
■ ^{Constant-Current Flyback Regulator}
■ ^{Constant-Current SEPIC Regulator}
■ ^{Thermo-Electric Cooler (Peltier) Driver}
Typical Application Circuit
Boost LED Driver
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